The mobile network, such as the global system for mobile communications (GSM) and the universal mobile telecommunications system (UMTS), etc., uses the circuit switch technology called as the circuit switched (CS) domain, which can provide the basic voice service for the users and the supplementary service based on the voice service.
In some places in the world, such as Africa, South America and South Asia, etc., there is a lack of fast and reliable transmission resources or high transmission cost exists, which brings certain difficulties to the network and service deployment for the operator. However, it can be obtained according to the statistical data that most of the calls in the mobile network are local calls in those places and these calls are generated in the same base station system (BSS). For the local calls, if the local switch technology (the voice data is looped in the BSS) is used, then the transmission resource of the A interface between the BSS and the mobile switch center (MSC) of the core network can be saved.
FIG. 1 is a schematic diagram of a traditional voice call. The user equipment (UE) accesses the BSS and the MSC through the CS domain. When the UE1 calls the UE2, the UE1 sends a call establishment request to its accessed MSC through the BSS; the MSC finds out the called UE2 according to the accessed location information of the UE2, and notifies the BSS to establish the radio bearer connecting to UE1 and UE2 and establish the bearers of the UE1 and UE2 between the BSS with the MSC respectively; the bearers at both sides of the MSC are looped, which ensures the voice communication between UE1 and UE2.
FIG. 2 is a schematic diagram of a voice call using local call local switch technology. Compared with FIG. 1, when receiving the call establishment request of the UE1, the MSC judges whether the UE1 and the UE2 belong to the same BSS according to a cell, and if the UE1 and the UE2 belong to the same BSS, then the MSC notifies the BSS to execute the local switch; the bearer loops of the UE1 and the UE2 are executed at the BSS side, which saves the bearer resources, namely the bearer resource of the A interface, between the BSS and the MSC.
FIG. 3 is a flow chart of signaling using local call local switch technology of FIG. 2, which comprises the following steps:
301, the UE1 and the UE2 initiate a call in the same BSS and establish the interconnection through the MSC of the core network, and the MSC allocates the circuit numbers or the call identifiers between the BSS and the MSC to the calling UE1 and the called UE2;
302, the called UE2 replies in the ringing state and sends the called reply message through the BSS to the MSC;
303, the MSC sends the called reply message to the calling UE1 to notify the UE 1 that the call is connected;
304, the MSC judges whether this call is a local call which belongs to the same BSS according to the current location information of the calling UE1 and the called UE2;
305, if the call is a local call which belongs to the same BSS, then the MSC sends the local switch command message including the circuit numbers or the call identifiers between the BSS and the MSC allocated to the calling UE1 and the called UE2 by the MSC to the BSS to notify the BSS to execute the local switch;
306, the BSS receives the local switch command message and associates the two ongoing communication sessions according to the circuit numbers or the call identifiers of the calling UE1 and called UE2 in the local switch command message, and their voice data bearers are looped to implement the switch of the voice bearers in the BSS;
307, the BSS sends the local switch success message to the MSC after the local switch succeeding; and
308, the MSC, after receiving the local switch success message, notifies BSS to release the voice bearer connection between the BSS and the MSC, that is, release the bearer connection of the A interface.
With regard to the analysis in the above steps, if it is in a scenario that the BSS connecting multiple MSCs, as shown in FIG. 4, the calling UE1 accesses the MSC 1 through the BSS and the called UE2 accesses the MSC 2 through the BSS, although the calling UE1 and the called UE2 initiate the call in the same BSS, the calling UE1 and the called UE2 access the different MSCs respectively, thereby causing that neither MSC1 accessed by the calling UE1 nor the MSC2 accessed by the called UE2 can judge whether this call is a local call according to the location information of the calling UE1 and the called UE2 in step 304, and finally causing the problem that the local call cannot execute the local switch.